Impulsivity has been thought of as leading to or being the result of prolonged drug abuse (cocaine and alcohol addiction, gambling). Others have suggested that prolonged (prenatal) exposure to environmental toxicants (lead, for instance) may result in impulsive behavior, which may then facilitate further drug abuse, or hamper 'normal' development. Thus, impulsivity is an important behavioral phenomenon the etiology of which is currently poorly understood, as it has not received much experimental attention up until recently. Therefore, it is timely to consider the different methods used to study impulsive behavior and to understand the strengths and limitations of each. Both animal models and applications in the human behavioral laboratory need to be carefully scrutinized. The proposed symposium offers a framework within which this will be accomplished. All participants are actively involved in the study of impulsive behavior either in the animal laboratory or in applied settings. Dr. Evenden will discuss his pioneering work on the role of 5-HT in impulsive behavior and his interest in genetic factors that may modulate drug effects on impulsive behavior. Dr. Richards developed the innovative experimental paradigms to study indifference in experimental animals, including humans. Dr. Brockel will discuss her work on in toxicant exposure that may lead to changes in attention and impulsive behavior. Dr. van Haaren will address sex differences in the areas of impulsivity and self-control. Dr. Chelonis will contribute his work aimed at validating animal models of impulsive behavior in clinical settings. Dr. Bickel will share his expertise with respect to the application of animal models to research settings in which impulsivity can be assessed in drug-dependent human subjects. The symposium will take place at the annual meeting of the Behavioral Toxicology Society (June 25 and 26, 2000) in Palm Beach. FL.